Typically, as a technique to improve an output of an engine, a method (supercharging) of compressing intake air with a supercharger such as a turbocharger and supplying an engine with the compressed intake air is known, and widely used in an engine for an automobile and the like.
A turbocharger normally includes a rotary shaft, a turbine impeller disposed on an end side of the rotary shaft, a compressor impeller disposed on the opposite end side of the rotary shaft, and a bearing housing which accommodates a bearing for rotatably supporting the rotary shaft. The rotary shaft rotates at a high speed in response to exhaust energy of exhaust gas being applied to the turbine impeller, and thereby the compressor impeller disposed on the opposite end side of the rotary shaft compresses intake air.
For the bearing rotatably supporting the rotary shaft, lubricant oil is supplied to clearance between the rotary shaft and a bearing surface. A seal ring is disposed between the outer peripheral surface of the rotary shaft and the inner peripheral surface of the bearing housing to prevent leakage of the lubricant oil along the rotary shaft. The seal ring has an outer peripheral surface contacting the inner peripheral surface of the bearing housing due to elasticity, and has an edge surface contacting a bearing-side wall surface of a seal groove formed on the outer peripheral surface of the rotary shaft due to a pressure of high-pressure gas, thereby sealing the clearance between the outer peripheral surface of the rotary shaft and the inner peripheral surface of the bearing housing.
Further, the seal ring also has a function to prevent leakage, along the rotary shaft, of high-pressure exhaust gas to be supplied to the turbine impeller, and high-pressure intake gas compressed by the compressor impeller.
The seal ring is formed from an elongated seal member processed into a ring shape, and has a butting section where opposite end surfaces of the seal ring are adjacent but have a gap between each other. Thus, with only one seal ring provided, it would be difficult to completely eliminate leakage of a fluid through the butting section. Accordingly, there is a technique that provides two seal rings.
In a seal structure provided with two seal rings, one of the seal rings is disposed by the side of an impeller which is subject to action of high-pressure gas, and is pressed against a bearing-side wall surface of a seal groove formed on an outer peripheral surface of a rotary shaft. In such a structure, however, a seal ring may become worn, which may deteriorate durability of the seal ring. Patent Documents 1 and 2 disclose a seal structure as a typical technique to solve the above problem.
Patent Document 1 discloses a seal structure with two seal rings, the first seal ring and the second seal ring, disposed between an outer peripheral surface of a rotary shaft and an inner peripheral surface of a bearing housing. The seal structure of patent Document 1 further includes a stopper disposed between the first seal ring and the second seal ring. The stopper is to restrict movement of the second seal ring disposed by the side of an impeller toward the first seal ring. The stopper reduces a pressing force applied by high-pressure gas from the impeller to press the second seal ring against a bearing-side wall surface (the second cylindrical portion) of a seal groove formed on the outer peripheral surface of the rotary shaft, thereby suppressing wear of the second seal ring.
Patent Document 2 discloses a seal structure with two seal rings, the first seal ring and the second seal ring, disposed between an outer peripheral surface of a rotary shaft and an inner peripheral surface of a bearing housing. In the seal structure of Patent Document 2, the second seal ring by the side of an impeller has a seal width broader than the width of a partition wall formed between the first seal ring and the second seal ring. If wear of the second seal ring develops as the second seal ring is pressed against the partition wall by high-pressure gas from the impeller, the second seal ring partially extends beyond the partition wall to contact the first seal ring. Accordingly, a pressing force which presses the second seal ring against the partition wall is reduced, and further development of wear on the second seal ring is suppressed.